Originally Posted by John07
Yes that's correct, on my car there are drains on both sides.
Yes there are drain spigots on both sides of mine too but you will see that the form of the airbox is different on mine to accommodate the aircon evaporator. The principal of blocking hot engine bay air (and potential fumes) remains the same for aircon and non aircon systems.

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Foam cut to shape to fit the top of the airbox.

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I made the blocking piece from a sheet of PVC cut and bent into shape. Where the material was bent a crack opened but it is only in the upper surface and I will use a little black silicon to fill it. If ever I replace it I will probably use a piece of aluminium instead now that I have the shape needed.

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Blocking piece in place.

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How it looks after a few years of use. Note the impression left by the edge of the louvres. It only just covers the edge. Probably the louvres should have been placed a centimetre closer to the hinge.

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Tube fitted to lower left-hand drain spigot. I only worried about the left-hand side because condensed water from the aircon evaporator was getting under the ECU cover and dripping into the footwell past the main cable grommet (the one where all the cables pass through to the back of the dash). The dried leaf is an optional extra laugh

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Showing the neoprene gasket that I place under ECU cover flanges. The idea is to stop possible ingress of water that could then drip into the footwell. After taking the photo I noticed that the cable grommet was a little out of place. I have fixed it smile

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This shows the drain tubes at the bottom of the in-cabin part of the air system. If they do not exist it would be possible to fit them but it would not be easy with the gearbox cover in place. Even in cars without aircon I believe these drains would be desirable due to the possible ingress of rain water.
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This last photo shows an example of poor design that creates long runs of tube but, worst of all, the tube from the compressor to the evaporator has a section which runs behind the hot radiator. This could be resolved by swapping the position of the compressor and the alternator.. The tubes which run to the condenser (aircon radiator) that is positioned in front of the radiator are also excessively long and whilst this is not a problem for the system it is untidy and unnecessary. It is indicative of a "near enough is good enough" attitude to fitting the aircon system.